Cannot bind NSSlider in IB?

Question

I just created a new Xcode project. In the AppControl class Header file I have the following objects defined (and some other ones, too):

    IBOutlet NSImageView *inputImageView;
    IBOutlet NSImageView *outputImageView;      
    IBOutlet NSTextField *myNoiseLevel;
    IBOutlet CGFloat *mySharpness;

After putting the basic code into the .h and .m files, I then went into Interface Builder and created my UI. I was able to bind the two NSImageView controls in IB to the corresponding NSImageView objects listed above. And I was able to bind a couple of other objects/controls, also. But I am NOT able to bind the last two items listed (myNoiseLevel and mySharpness) to the NSSlider controls I have on the application main window. I'm not sure why. I know this kind of thing is probably hard to diagnose, because it is not "strictly code related," but if there is something "tricky" about binding sliders please let me know what the main "suspects" are that I should check.

This is my first attempt to use a slider control through IB. I have a book (Cocoa programming for Mac OS X, 3rd ed., by A. Hillegass) that I am using to learn about the basic way to do this stuff. And he has a slider example in there. But his slider example is "continuous" and it uses key path binding. I think this is overkill for what I want/need to do -- I just want to pull the value from the slider when another button is pushed (no need for "continuous" update). So I am trying to directly bind the "outlets" listed when I right-click on my App Control object (one for each of those items shown above), to the slider controls on my window. But when I cntl-drag from the AppControl outlet up to the corresponding slider, the slider will not "accept" the arrow I'm dragging.

Does this make sense? Any idea what I'm doing wrong and/or what I need to do to make the binding work? I have tried saving / building / closing & reopening IB and Xcode -- all to make sure IB has the latest version of everything. Still no luck, though.

One last thing ... What I really need are CGFloat numbers, from the slider. Can I simply declare the Outlet as CGFloat type ... or do I need to define it as NSTextField (or something else), and then convert it to Float in my program? You can see in the IBOutlets I pasted above, that I was trying different data types for the outlets (trying to see if my defining them as CGFloat was somehow preventing the bindings).

Answer 1

Make the outlet an NSSlider*. You should then be able to connect to it. When you need the value (eg, in response to the button press you mention) call [yourSliderOutletName doubleValue].

More generally: an IBOutlet is an ivar that can be filled in with a pointer to the actual object awoken from a NIB file. As such, it needs to be of an appropriate type to hold that pointer -- the object's actual class, or one of its superclasses or protocols, or (least informatively) id. You can't just arbitrarily connect an object to any old variable, like your CGFloat. There's no implicit conversion -- how is the system supposed to know what you want?